All-time low in Florida, numbers receding (5)
I believe the answer is:
Here is my best explanation:
'all-time low' is the definition.
(I've seen this before)
'in florida numbers receding' is the subsidiary indication.
'in' indicates a hidden word.
'receding' says the letters should be written in reverse.
'ridan' is hidden within 'florida numbers'.
'ridan' backwards is 'nadir'.
(Other definitions for nadir that I've seen before include "Given lowest place", "Floor of drain in need of repair", "Point opposite the zenith", "Deepest point", "Rock bottom", "The lowest point to drain into", "You can't sink lower!", "Very bottom, farthest from zenith", "Drain (anag)" and "Lower one cannot get!".)